Presentation on theme: "Chapter 8 Weathering, Soils and Weathering, Soils and Mass Movement BFRB Pages 157 - 161."— Presentation transcript:
Chapter 8 Weathering, Soils and Weathering, Soils and Mass Movement BFRB Pages
Weathering and Erosion Weathering - Def. - the break down of rocks that have been exposed to the atmosphere.Weathering - Def. - the break down of rocks that have been exposed to the atmosphere. Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion.Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion. Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity.Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity. VIF - Most erosion that takes place on Earth is caused by moving waterVIF - Most erosion that takes place on Earth is caused by moving water
What is W.E.D.? Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes.Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes. Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is called Erosion.Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is called Erosion. Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.
Remember the Rock Cycle Diagram? Page 6 of the Handy Dandy ESRTs…
2 Types of Weathering Chemical weathering Chemical weathering – rocks break down as their minerals change in chemical composition (they become different substances). Physical weathering Physical weathering – rocks are broken down into smaller pieces without changing their chemical composition (what theyre made of). AKA - mechanical weathering
Agents of Physical Weathering
Types of Physical Weathering #1 - Frost action (aka Ice Wedging)#1 - Frost action (aka Ice Wedging) –water enters small cracks in the rock. –when water freezes, it expands and forces the crack to open more. –the ice melts back into liquid water and fills the crack again. –the process repeats over and over again until the rock breaks apart.
Mt. Brewster – looks solid, right?
Close up shows jagged rocks from FROST wedging!
This boulder has been split apart by frost action!!!
Types of Physical Weathering #2 - Abrasion#2 - Abrasion –It is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in windy areas, under glaciers, or in stream channels. –It can also happen during rock slides (gravity)
Rocks that have undergone different kinds of abrasion look very differently! Rock weathered by a rockfallRock weathered by a stream
Types of Physical Weathering #3 Plant Roots#3 Plant Roots The roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!
Types of Physical Weathering #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.
Types of Physical Weathering #5 Wetting and drying#5 Wetting and drying –Breaks up rocks that are made from clay. –When they are wet they expand, and they shrink as they dry. –As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!
Types of Physical Weathering # 6 - Exfoliation# 6 - Exfoliation –soil and rock is removed (glaciers or uplifting), exposing rock found deep underground. –This releases the pressure causing the surface of the rock to expand and eventually crack and flake off.
Agents of Chemical Weathering
#1 - Hydrolysis#1 - Hydrolysis –water (hydro) reacts with minerals such as feldspar and hornblende to form clay which weakens the rock and breaks it apart.. Link to visualization
#2 - Plant Acids - Lichen & Moss These plants live and grow on rocks and eventually break them apart by the weak acids that they secrete! Agents of Chemical Weathering Lichen – light green/looks like bread mold Moss – dark green
Agents of Chemical Weathering #3 - Oxidation#3 - Oxidation –oxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide). – The rusty spots weaken the rock and it breaks apart. –Water is not needed for oxidation to occur, but it does speed up the process!
Chemical weathering of basalt - an iron rich (mafic) igneous rock! You see, it all comes together!!!
Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)
Agents of Chemical Weathering #4 - Acids in water#4 - Acids in water –Carbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid. –This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble! –Acids may be found in ground water (forms caves) or in rain water (acid rain).
Gnarled Rock – a formation of limestone chemically weathered by acid rain
Pitted limestone from rainfall
Carbonic acid in groundwater causes caves to form.Carbonic acid in groundwater causes caves to form. –When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed. –Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations
Carlsbad Caverns – New Mexico Stalactites Stalagmites
Rates of Weathering
Factors that affect rates of weathering: Rocks resistance to weathering (HARDNESS) Amount of surface area Climate: –Chemical weathering occurs faster in warm, wet climates –Mechanical weathering occurs faster in cold or dry climates
The central area of rock was less resistant to weathering…thus the arch was formed! This is differential weathering.
Devils Tower, Wyoming - An igneous intrusion (volcanic neck – the underneath of the volcano) surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is an example of differential weathering!!! You may recognize it if youve ever seen Close Encounters of the Third Kind
Surface Area Greater surface area increases the rate of weathering Surface area is the amount of rock surfaces exposed to the atmosphere Weathering creates more surface area
Dry Climate = Mechanical Weathering! Devils Marbles, Australia – Mechanical weathering from wind and sand!
Wet Climate = Chemical Weathering! (water speeds up chemical reactions) Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!
Soil has 4 components: Weathered rock Weathered rock Organic material (humus) Organic material (humus) Air Air Water Water What is soil made of?
There are 2 types of soil…. PARENT MATERIAL is the rock that the soil forms from When the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still resides or lives with the parent material) When the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still resides or lives with the parent material) If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOIL If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOIL VIF - MUCH OF THE SOIL IN NYS IS TRANSPORTED SOIL LEFT BEHIND BY GLACIERS!
Cross section of soil layers Each layer is called a HORIZON Horizon O/A = Topsoil (mostly humus, some weathered rock) Horizon B = Mostly weathered rock, some organic material (mineral rich zone) Horizon C = Broken Bedrock BEDROCK
HORIZON A HORIZON B HORIZON C
MASS MOVEMENTS MOVEMENTS OF SOIL, ROCK, AND LOOSE MATERIALS CAUSED BY THE FORCE OF GRAVITY
CREEP ( Slow Mass Movement) Very slow downward movement of soil –Only noticeable by the results of trees, fence posts, telephone poles, etc… that are tilted downhill
LANDSLIDE (Rapid Mass Movement) Sudden movement of soil downhill (usually a very steep slope)Sudden movement of soil downhill (usually a very steep slope) –AVALANCHE – landslide made of Ice & Snow as well as Soil –SLUMP – small areas of land moving downhill - especially along roadways that cut into the side of hills
MUDFLOW or LAHAR (Rapid Mass Movement) Very fast & dangerous movement of water saturated soil (MUD)
Even though rapid mass movement is more noticeable than slow mass movement, overall, more material is transported via creep than all others combined – because it is occurring in many more places and all the time!!!!